Increased engine noise due to exhaust riser closing??

[sailingdeacon]

Sorry if this has been asked, I could not find it. My engine noise is louder than in previous years. This only occurs at idle. With an increase in rpms there is little noise. Could it be that the exhaust riser arm is becoming clogged where the water comes in but with increased rpms more water is forced through it? Water pump impeller is OK.

A second symptom is that the rpms under load is about 300 rpms lower than in previous times. I get full rpms without any load.

At idle, water is coming out the exhaust but I cant tell if it is a normal flow.
Engine is an M35 4 cyl Universal with a water lift muffler fresh water cooled engine.

Engine does not overheat.

Does an increased exhaust noise indicate

 

[sailingdeacon]

The exhaust riser has 325 hours on it, which I would not have thought would be enough time for closure. I took the hoses off and looked up into the riser near where the water would come in andthere are several mounds of calcium or whatever. I could not tell for sure but it maybe the hole for water is restricted. Cant really see it, but a 1/4 inch hose inserted in the top was hard to push through... although there is a severe turn in the passage way.

 

[footrope]

Some older exhaust hoses have a silicone inner liner that can separate from the carcass of the hose (rubber/cloth/wire) and cause blocking, as mine did a few years ago. The newer hoses I've used (Trident is one brand) don't seem to have that type of construction. The symptoms you describe are similar to what I experienced - loss of power at the usual RPM, etc. This hose was between the exhaust elbow and the muffler.

Might be worth a look.

 

[Glyn Judson]

Hose collapse.

Craig and all, Interestingly, the same thing happened to my raw water intake several years ago. All appearances were that the hose was in good condition but for the fact that I had a greatly diminished amount of water coming out the exhaust. That was the first clue and a couple of over heating alarms and red lights confirmed it. On a hunch, thinking that there might be something blocking the intake hose(s), I replaced them all and magically full water flow was restored. Ironically, I'm now facing the same dilemma with the main tank fresh water fill hose. It takes only seconds for the hose to indicate that the tank is full when I know better and the only way now to fill it is through the auxiliary tank fill on the foredeck, filling them both at the same time. Filling is much slower that way because of the small hose joining the two tanks. My problem now is that I'm too big a guy to fit down into the port lazarette in order to reach up to side deck where the hose attaches to the deck fill, etc. Well I guess it's time to take Marilyn out to dinner for no good reason and spring the question, "My love, will you help me with a little project on the boat?" It's all great fun, Glyn AND Marilyn Judson, E31 hull #55, Marina del Rey, CA